The present invention relates to a seat belt retractor including an energy mechanism (that is, an absorbing belt load limiting mechanism, which is also hereinafter referred to as the xe2x80x9cEA mechanismxe2x80x9d) which, at a normal time, winds up a webbing so that it can be retracted and extracted, and which, during an emergency, such as collision of a vehicle, prevents the webbing from being extracted or withdrawn, and which, when the drawing out of the webbing is prevented, limits the load exerted on the webbing by twisting and deformation of a torsion bar, so that an impact energy is absorbed. More particularly, the present invention relates to a seat belt retractor in which a limited load (hereinafter referred to as the xe2x80x9cEA loadxe2x80x9d) which limits the load exerted on the webbing is set so that it can be varied.
In this type of a conventional seat belt retractor, when a webbing is restrained to protect an occupant of a vehicle in an emergency, such as collision of the vehicle, the vehicle is considerably decelerated, so that the occupant tries to move forward due to a large amount of inertia. Therefore, a large load is exerted on the webbing, so that the occupant receives a large impact force from the webbing. Although this impact force with respect to the occupant does not particularly cause any problems, it is desirable that this impact force be limited if possible.
To achieve this, conventionally, an EA mechanism including a torsion bar has been provided. In an emergency, such as that mentioned above, the torsion bar is twisted and deformed, and absorbs impact energy produced by impact force in order to limit the load exerted on the webbing. In order to effectively absorb the impact energy, various proposals have been made to variably set the EA load.
One example of this type of a conventional seat belt retractor including such an EA mechanism that variably sets the EA load is disclosed in, for example, Japanese Unexamined Patent Publication (KOKAI) Nos. 2000-16243 and 2000-25567. The seat belt retractors disclosed in these documents are each constructed so that a second torsion bar is disposed inside a cylindrical first torsion bar, and the two torsion bars are linked at corresponding end portions to rotate in at least a direction of rotation. In an emergency, when the torsion bars are twisted and deformed, at first, the first and second torsion bars are both twisted and absorb a large amount of impact energy. When the first torsion bar ruptures, the impact energy is absorbed by twisting the second torsion bar alone. Accordingly, the EA load is varied in two stages.
Another example of this type of a conventional seat belt retractor including such an EA mechanism that variably sets the EA load is disclosed in, for example, Japanese Unexamined Patent Publication (KOKAI) No. 10-258702. In the seat belt retractor disclosed in this document, a shaft is disposed at the inner portion of a cylindrical spool that winds up a webbing, and an EA plate which is disposed inside a space formed between the spool and the shaft, and has a double-curvature shape and a control structural portion, is provided. One end of the EA plate receives a rotational force of the spool in a direction in which the webbing is extracted. The other end of the EA plate is connected and secured to the shaft. During the relative rotation of the spool with respect to the shaft in the direction in which the webbing is extracted in an emergency, a rotational force of the spool in the direction in which the webbing is extracted acts on the one end of the EA plate, so that the EA plate undergoes plastic deformation. This causes impact energy to be absorbed, and deformation force to be changed by the control structural portion, that is, energy absorption to be changed. In this way, the EA load is made variable.
Still another example of this type of the conventional seat belt retractor including such an EA mechanism that variably sets the EA load is disclosed in, for example, Japanese Unexamined Patent Publication No. 2000-43677. The seat belt retractor disclosed in this document comprises a torsion bar, which is provided in a spool, and a stopper ring, which is provided at a side surface of the spool. During the relative rotation of the spool with respect to a pawl holder in a direction in which the webbing is extracted at the time of an emergency, at first, the torsion bar is twisted and an engaging stepped portion of the pawl holder cuts an inner peripheral side of the stopper ring in order to absorb a large amount of impact energy. When the cutting of the inner peripheral side of the stopper ring is completed, the impact energy is absorbed by twisting the torsion bar alone. In this way, the EA load is made variable in two stages.
The EA load may be made variable by using the following structure instead of the structure that makes it variable by cutting the inner peripheral side of the stopper ring. This structure comprises a shear pin or a shear protrusion at a side surface of the spool. In this structure, at first, the torsion bar is twisted and a shear load is exerted onto the shear pin or the shear protrusion in order to absorb a large amount of impact energy. After the shear pin or the shear protrusion has been ruptured by shearing, impact energy is absorbed by twisting the torsion bar alone. This causes the EA load to be made variable.
However, in the above-described EA mechanism using two torsion bars, since the axial length of the first torsion bar to be ruptured is set equal to the main axial length of the second torsion bar, the EA load depends upon the axial length of the second torsion bar. Therefore, the EA load can not be set freely, and it is difficult to arbitrarily set the EA load regardless of the axial length of the second torsion bar.
In the above-described EA mechanism using the EA plate having the control structural portion, not only does the EA plate have a complicated double-curvature form, but also the EA mechanism has a complicated structure. Moreover, since the form of the EA plate and the structure of the EA mechanism are complicated, and the control structural portion is formed by local work hardening, it is difficult to stably set the EA load.
In the EA mechanism in which the inner peripheral side of the stopper ring is cut, it is difficult to always stably set the EA load by cutting the inner peripheral side of the stopper ring.
In view of the above-described situations, it is an object of the present invention to provide a seat belt retractor which, by a relatively simple structure, makes it possible to set an EA load more freely and to more stably set the EA load.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To overcome the above-described problems, in a first aspect of the invention, a seat belt retractor comprises at least: a spool which winds up a seat belt; a lock mechanism including a locking member whose rotation in a direction in which the seat belt is extracted or withdrawn is prevented in an emergency; and a seat belt load limit mechanism including a torsion bar disposed in the spool. The torsion bar rotatably connects the spool and the locking member and is twistable and deformable. When the rotation of the locking member in the direction in which the seat belt is extracted is prevented in order for the spool to rotate relative to the locking member in the direction in which the seat belt is extracted, the load limit mechanism limits a load that is exerted on the seat belt by the twisting and deformation of the torsion bar. The seat belt load limit mechanism further includes a torsion pipe disposed inside an annular space between the spool and the torsion bar. One end side of the torsion pipe is connected and secured to the spool and the other end side of the torsion pipe is provided so as to be engageable with and disengageable from the locking member, or the one end side of the torsion pipe is provided so as to be engageable with and disengageable from the spool and the other end side of the torsion pipe is connected and secured to the locking member. When, at a normal time, the engageable and disengageable end side of the torsion pipe engages a member for engagement with the engageable and disengageable end side in a direction of rotation and when the spool rotates relative to the locking member in the direction in which the seat belt is extracted, the load exerted on the seat belt is limited by the twisting and deformation of the torsion pipe, and the engageable and disengageable end side of the torsion pipe moves out of and is disengaged from the member which engages the engageable and disengageable end side by contraction of the torsion pipe in an axial direction caused by the twisting and the deformation of the torsion pipe.
According to a second aspect of the invention, the engageable and disengageable end side of the torsion pipe includes an axially extending engaging protrusion, and the locking member or the spool includes an engaging recess which engageably and disengageably receives the engaging protrusion. When, at a normal time, the engaging protrusion is inserted into the engaging recess and engages the engaging recess in the direction of rotation and the spool rotates by a predetermined amount relative to the locking member in the direction in which the seat belt is extracted, the engaging protrusion moves out of the engaging recess.
According to a third aspect of the invention, the torsion pipe includes a torsion performance control portion that controls the torsion performance of the torsion pipe.
According to a fourth aspect of the invention, the torsion performance control portion of the torsion pipe includes a hole that passes completely through the torsion pipe from an outer peripheral surface to an inner peripheral surface of the torsion pipe, or a recess that does not pass completely through the torsion pipe from the outer peripheral surface to the inner peripheral surface of the torsion pipe.
According to a fifth aspect of the invention, a side edge of the engaging protrusion formed downstream in a direction in which a webbing is extracted and a side edge of the engaging recess formed downstream in the direction in which the webbing is extracted are inclined.
According to a sixth aspect of the invention, the seat belt retractor further comprises torsion pipe position control means which, when the engageable and disengageable end side of the torsion pipe is disengaged from the member which engages the engageable and disengageable end side, moves the torsion pipe in a direction in which the engageable and disengageable end side of the torsion pipe moves away from the member which engages the engageable and disengageable end side.
According to a seventh aspect of the invention, the torsion pipe is provided between the spool and the locking member with the torsion pipe being previously twisted by a predetermined amount in a direction opposite to a direction of the twisting and deformation of the torsion pipe.
In the seat belt retractor of the present invention having such a structure, when the rotation of the locking member is stopped due a large deceleration of a vehicle that is produced in, for example, a collision of the vehicle, and when, by a webbing drawing-out load, the spool rotates relative to the locking member in the direction in which the webbing is extracted, the torsion bar and the torsion pipe are twisted and deformed. This causes impact energy to be absorbed by the torsion bar and the torsion pipe. The torsion pipe is contracted in the axial direction as a result of being twisted and deformed, so that the engageable and disengageable end side of the torsion pipe moves axially in the direction in which it disengages from a member (such as the locking member or the spool) that engages this end of the torsion pipe. When the spool rotates relative to the locking member by a predetermined amount, the engageable and disengageable end side of the torsion pipe disengages the member that engages this end side of the torsion pipe. This causes completion of the twisting and deformation of he torsion pipe, after which the torsion bar alone is continually twisted and deformed, so that impact energy is absorbed by twisting and deforming the torsion bar alone. Accordingly, the limit load of the seat belt load limit mechanism varies in two stages from a limit load based on the twisting and deformation of both torsion bar and torsion pipe and a limit load based on the twisting and deformation of the torsion bar alone.
In the torsion pipe used in the present invention, not only the thickness, the material, and the pipe diameter can be arbitrarily selected, but its axial length can also be set regardless of the axial length of the torsion bar. Therefore, the limit load can be set freely. In addition, since the torsion pipe can be formed using a simple pipe structure, the structure of the seat belt load limit mechanism can be simplified, and the limit load is more stably set.
In particular, in the seat belt retractor according to the second aspect of the invention, the mechanism that engages and disengages the torsion pipe and the locking member or the spool, comprises an engaging protrusion formed on the torsion pipe and an engaging recess formed in the locking member or the spool, so that the structure of the seat belt load limit mechanism is further simplified.
In the seat belt retractor according to the third aspect of the invention, a torsion performance control portion is provided at the torsion pipe. By the torsion performance control portion, the torsion pipe can have any torsion performance. Therefore, the EA load can be set more freely.
In the seat belt retractor according to the fourth aspect of the invention, the torsion performance control portion is formed by a hole that passes completely through the torsion pipe from the outer peripheral surface to the inner peripheral surface of the torsion pipe or by a recess that does not pass completely through the torsion pipe from the outer peripheral surface to the inner peripheral surface of the torsion pipe. By arbitrarily setting the width of the hole or the recess, the axial length of the hole or the recess, the tilt angle of the hole or the recess with respect to the axial direction of the torsion pipe, and the number of holes or recesses, any torsion performance of the torsion pipe can be easily provided, the torsional performance control portion can be easily formed by a hole or a recess, and the structure of the torsion performance control portion is simplified. Moreover, since the hole or recess is easily formed, the EA load can be more stably set.
In the seat belt retractor according to the fifth aspect of the invention, since the side edge of the engaging protrusion at the downstream side in the direction in which the webbing is extracted and the side edge of the engaging recess at the downstream side in the direction in which the webbing is drawing are inclined, when the torsion pipe is twisted and moves in the direction in which the engaging protrusion moves out of the engaging recess, the engaging protrusion gradually moves axially in the direction in which it moves out of the engaging recess while it gradually rotates in the direction in which the webbing is extracted by the inclined surfaces. This makes it possible for the limit load to vary smoothly when changing from a limit load based on the torsion bar and the torsion pipe to a limit load based on the torsion bar alone.
In the seat belt retractor according to the sixth aspect of the invention, when a vehicle is considerably decelerated in, for example, a collision of the vehicle, the torsion pipe position control means causes the torsion pipe to move so that the engageable and disengageable end side of the torsion pipe moves away from the member that engages this end side of the torsion pipe. Therefore, the engageable and disengageable end of the torsion pipe will not re-engage the member that has engaged this end, so that a stable EA load can be obtained.
In the seat belt retractor according to the seventh aspect of the invention, since a spool stroke when the EA load is applied by the torsion bar and the torsion pipe is increased, impact energy can be more effectively absorbed.